Generally, a bumper reinforcement equipped in a bumper device for a vehicle is mounted to an impact absorber such as a crash box, or the like, provided at an end portion of a front side member or a rear side member of a vehicle frame. For example, JP2001-58550A discloses a bumper device for a vehicle including a bumper reinforcement having a working hole at an impact surface thereof. The working hole is used when the bumper reinforcement is mounted to the impact absorber.
In a condition where the bumper reinforcement is mounted to a heavy vehicle, a higher degree of section stiffness is designed. However, if the section stiffness is increased, stress may easily be concentrated in the vicinity of the working hole formed at the impact surface in a condition where the vehicle collides against a collision object at an angle. Further, a rupture may occur from the working hole.
For example, the Insurance Institute for Highway Safety (i.e., IIHS) executes a crash safety performance test in which the vehicle collides against a 30 degree offset barrier at 5 mph. Also in this test, there is a possibility of occurring the rupture at the bumper reinforcement. If the rupture occurs, energy absorption at the bumper reinforcement may not sufficiently be performed. Further, a stroke at a vehicle body side for the impact absorption may be increased and a repair cost may thereby be increased.
The present invention has been made in view of the above circumstances, and provides a bumper device for a vehicle, which restrains a generation of rupture from a hole formed on an impact surface of a bumper reinforcement at the time of a vehicle crash.